Animal Muscles

myofibrils bands of actin and myosin together appear

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Unformatted text preview: ; bands of actin and myosin together appear darkest. Transmission-EM How Do Muscles Contract? The sliding filament mechanism of muscle contraction: • Myosin heads can bind specific sites on actin molecules to form cross bridges. Myosin changes conformation, causes actin filament to slide 5–10 nm. ! Sliding Filaments! Actin and Myosin Filaments Overlap to Form Myofibrils Actin monomer! Single sarcomere! Myosin filament! Tropomyosin! Troponin! Actin filament! Globular head! Myosin molecule! Linear polypeptide chain! 47.1 How Do Muscles Contract? A neuromuscular junction is the “chemical synapse” between a motor neuron and a muscle cell. ! Muscle cells are excitable: the plasma membrane can conduct action potentials. Acetylcholine is released by the motor neuron at the neuromuscular junction and opens ion channels in the motor end plate. ! Figure 44.13 Synaptic Transmission Begins with the Arrival of a Nerve Impulse! The Neuromuscular Junction acetylcholine! Skeletal muscle fibers ! Axon terminals ! =Na+ channels! 47.1 How Do Muscles Contract? Action potentials also travel deep within muscle fiber via T tubules. T tubules (transverse tubules) descend into the sarcoplasm (muscle fiber cytoplasm). T tubules run close to the sarcoplasmic reticulum (ER): a closed compartment that surrounds every myofibril. ! 47.1 How Do Muscles Contract? 47.1 How Do Muscles Contract? Sarcoplasmic reticulum: •  Fancy name for the endoplasmic reticulum of Actin filaments also include tropomyosin and troponin. muscle cells. •  Has Ca2+ pumps. At rest there is high concentration Troponin has three subunits: one binds actin, one binds myosin, and one binds Ca2+. of Ca2+ in the lumen of the sarcoplasmic reticulum. •  An action potential will open the Ca2+ channels, Ca2+ flows out of sarcoplasmic reticulum and triggers interaction of actin and myosin. ! At rest, tro...
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This note was uploaded on 02/13/2014 for the course MCDB 1B taught by Professor Weimbs during the Winter '08 term at UCSB.

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